1. Field
Embodiments of the invention relate to the field of surgical instruments; and more specifically, to surgical shears supported by an elongated tube-like member intended for use in minimally invasive surgeries.
2. Background
Minimally invasive surgery (MIS) (e.g., endoscopy, laparoscopy, thoracoscopy, cystoscopy, and the like) allows a patient to be operated upon through small incisions by using surgical instruments supported by an elongated tube-like member introduced to an internal surgical site. Generally, a cannula is inserted through the incision to provide an access port for the surgical instruments. The surgical site often comprises a body cavity, such as the patient's abdomen. The body cavity may optionally be distended using a clear fluid such as an insufflation gas. In traditional minimally invasive surgery, the surgeon manipulates the tissues by using hand-actuated end effectors of the elongated surgical instruments while viewing the surgical site on a video monitor.
The elongated surgical instruments will generally have an end effector in the form of a surgical tool such as a scissors, a forceps, a clamp, a needle grasper, or the like at one end of an elongate tube. An actuator that provides the actuating forces to control the end effector is coupled to the other end of the elongate tube. A means of coupling the actuator forces to the end effector runs through the elongate tube. To minimize the size of incision needed for the instrument access port, the elongate tube is generally of a small diameter, preferably about 6 millimeters. Thus, it is necessary that the means of coupling the actuator forces to the end effector be compact.
It may be desirable that the elongate tube be somewhat flexible to allow the surgical instrument to adapt to the geometry of the surgical access path. In some cases, the elongate tube may be articulated to provide access to a surgical site that is not directly in line with the surgical access port. It may be desirable to use wires as the means of coupling the actuator forces to the end effector because of the flexibility they provide and because of the ability of a wire to transmit a significant force, a substantial distance, through a small cross-section. However, an unsupported wire is only able to transmit a force in tension. Thus it is generally necessary to provide two wires to transmit a bidirectional actuating force. This doubles the cross-section required for the wires to pass through the elongate tube.
The wires need to have sufficient strength to provide the tension necessary to create the required forces provided by the end effector. The more tension that is required, the larger the wire cross-section must be. Inefficiencies in converting wire tension into end effector forces increases the tension, and hence the cross-section, required. Increases in the cross-section, whether because of a greater number of wires or a larger cross-section of the individual cables, increases the effect of bending the cable, such as when is passes through an articulated wrist joint, on the force being delivered by the cable. This can cause changes in the closing force of a surgical end effector as the end effector is moved by an articulated wrist assembly that supports the end effector.
For surgical end effectors having two working parts that open and close relative to one another, such as the two blades of a pair of shears, it can be advantageous to route the force applying wires along the longitudinal axis of the tube and surgical end effector, continuing through the surgical end effector, around one of the two working parts, and then fixing the wire to the other working part. However, this is difficult with a conventional pair of shears that provides a fixed pivot point on the longitudinal axis of the surgical end effector joining the two cutting blades.
In view of the above, it would be desirable to provide a pair of surgical shears intended for use in minimally invasive surgeries that allows bidirectional actuating forces to be transmitted to the shears by wires routed along a longitudinal axis of an elongate tube and through the surgical shears.